Inorganic-Organic Composite Materials for Lithium Batteries

1 Results In order to develop high capacity anode materials for enhancing the performance of lithium-ion batteries,silicon (Si) and a variety of metals that alloy with lithium,such as Sn,Sb,and Al,were studied and found to be promising candidates as anode materials[1-4].Among them,Si appears to be the most attractive candidate due to its large theoretical lithium insertion capacity of 4 200 mAh g-1[1].Unfortunately,there is one severe problem with the application of Si anode,i.e., the large volume changes associated with alloying/de-alloying of lithium during electrochemical cycling,which causes great stress in the Si lattice,leading to cracking and crumbling of the Si particles,which results in abrupt failure of the electrode.To overcome the large volume changes and thus obtain better capacity retention and cycle life for Si anodes,one of the most promising approaches is to create a nanocomposite structure,in which nanosized Si particles are homogeneously dispersed in an electrically conducting matrix.Our group has demonstrated the potential of Si-C and Si-PPy for use as anode in Li-ion batteries.Carbon-coated Si nanocomposites were produced via a spray pyrolysis technique.Initially,the nanosized Si particles (<100 nm) were mixed in a citric acid/ethanol solution. This mixture was further spray-pyrolyzed in air at a low processing temperature,resulting in a homogeneous layer of carbon-coating on the surface of the spherical Si nanoparticles.High-resolution TEM images of the carbon-coated Si nanocomposites revealed an amorphous carbon layer on the Si particles’ surface,with the carbon-coating up to 7 nm thick.Carbon-coated Si nanocomposites can reversibly store lithium with both a high capacity of 1 500 mAh·g-1 and high coulombic efficiency above 99.5%,even after 20 cycles.Novel nano-silicon/polypyrrole composites were prepared by a chemical polymerization method with sodium p-toluenesulfonate (PTSNa) as the dopant and FeCl3 as the oxidant.TEM images of the samples show that the Si particles were uniformly distributed among the PPy particles.The PPy component in the composites effectively buffered the great volume changes during the cycling process.In the meanwhile,it acted as an efficient host matrix to prevent cracking and pulverization of the Si electrode due to phase transitions,thus improving the cyclability of the Si electrode.The Si/PPy composite electrodes maintained high activity and reversibility,even after 100 cycles.